Aircraft lateral guidance system

ABSTRACT

Course and directional radio signals are combined to produce an aircraft guidance signal. The guidance signal is amplified and applied to control the intercept of the aircraft with a directional radio beam. Circuitry is provided which is responsive to the radio signal for decreasing the aircraft angle of intercept to a preset minimum intercept angle as the aircraft approaches the radio beam. Upon intercept with the radio beam, the minimum intercept angle is reduced and the aircraft is directed along the radio beam. Also upon intercept with the radio beam, a cross wind correction is applied to the guidance signal. After a first preselected time interval from the intercept with the radio beam, the gain of the guidance signal is substantially reduced to provide a more comfortable flight. After a second predetermined time interval from intercept with the radio beam, the permissible bank angle of the aircraft is limited. A novel nonlinear circuit is provided in a feedback circuit to nonlinearly control the roll motor of the aircraft.

United States Patent 1191 Younkin AIRCRAFT LATERAL GUIDANCE SYSTEM [75]Inventor: James R. Younkin, Mineral Wells,

Tex.

[73] Assignee: Mitchell Industries, Inc., Mineral Wells, Palo PintoCounty, Tex.

22 Filed: Sept. 8, 1970, 211 Appl. No.: 70,250

52 us. or. 343 107, mm A 51 1111.131. G01s 1/16 [58] Field of Search343/108 R, 107;

[56] References Cited UNITED STATES PATENTS 6/1962 Rhodes et al 343/1077/1963 Medlinskiet al. 244/77 '8 X Primary Examiner-Benjamin A. BorcheltAssistant Examiner-RichardE. Berger Attorney-Richards, Harris & Hubbard22 2a COURSE) D :C

so 20/ RESET I hETWORK RADIO} 1111 3,739,382 June 12, 1973 [57] ABSTRACTCourse and directional radio signals are combined to produce an aircraftguidance signal. The guidance signal is amplified and applied to controlthe intercept of the aircraft with a directional radio beam. Circuitryis provided which is responsive to the radio signal for decreasing theaircraft angle of intercept to a preset minimum intercept angle as theaircraft approaches the radio beam. Upon intercept with the radio beam,the minimum intercept angle is reduced and the aircraft .is directedalong the radio beam. Also upon intercept with the radio beam, a crosswind correction is applied to the guidance signal. After a firstpreselected time interval from the intercept with the radio beam, thegain of the guidance signal is substantially reduced to provide a morecomfortable flight. After a second predetermined'time interval fromintercept with the radio beam, the permissible bank angle of theaircraft is limited. A novel nonlinear circuit is provided in a feedbackcircuit to nonlinearly control the roll motor of the aircraft.

19 Claims, 4 Drawing Figures 9O SECOND DELAY m TRANSMITTER BANK ANGLROLL RATE

BANK ANGLE LIMITER 3 Sheets-Sheet 1 RESET NETWORK Patented June 12, 1973COURSE,

RADIO,

INVENTOR:

JAMES R. YOUNKIN ATTORNEYS 9O SECOND DELAY SWITCH Wmgwwm 72 2o SECONDFLIP FLOP VALUE CIRCUIT 66 FIG. 2

' ABSOLUTE HIGH GAIN *AMPLIFIER Patented June 12, 1973 0230mm Qm ummzoo3 Sheets-Sheet 2 macs. @255:

Patented June 12, 1973,

3 Shuts-Shoot 5 Emmy NI x m 0 N56 AIRCRAFT LATERAL GUIDANCE SYSTEM FIELDOF THE INVENTION This invention relates to aircraft guidance, and moreparticularly to a method and apparatus for providing automatic lateralguidance for an aircraft with respect to a directional radio beam.

THE PRIOR ART A number of different types of systems have beenheretofore developed for controlling the lateral guidance of an aircraftas it approaches a directional radio beam. In many of these systems,course and radio sig nals have been mixed and utilized as guidancesignals aircraft guidance control. In many of these systems, a

plurality of series connected diodes have been utilized as nonlinearelements 'in order to provide a nonlinear action to the aircraft r ollcontrol motor. Such previous nonlinear diode circuits have thedisadvantage that they cannot easily be tailored or adjusted for usewith aircrafts with different operating capabilities or with aircraftroll control motors which have various thresh- I old operatingcharacteristics. Examples of prior systems with nonlinear diode circuitsare disclosed in the US. Pat. No. 3,555,39l, by James R. Younkin, filedMar. 1 l, 1966, and assigned to the present assignee.

SUMMARY OF THE INVENTION In accordance with the present invention, radioand course signals are combined and amplified for use in directing anaircraft toward a directional radio beam at a selected intercept angle.Circuitry is provided for introducing cross wind correction to theaircraft in response to intercept with the center line of the radiobeam. Circuitry is alsoprovided for reducing the gain of theamplification of the radio and course signals after a first preselectedtime interval from intercept with the radio beam. Circuitry is providedto limit the permissible bank angle of the aircraft after a secondpreselected time interval from the intercept with the radio beam; Inaccordance with another aspect of the invention, a combined directionalradio andcourse signal is amplified and utilized to control the guidanceof an aircraft toward an intercept with a directional radio beam and apredetermined intercept angle. Circuitry is responsive to the radiosignals for decreasing the angle of intercept to a preselected minimumintercept angle as the aircraft approaches the radio beam. Circuitry isresponsive to intercept with the radio beam for reducing the minimumintercept angle and for directing the aircraft along the radio beam. 7

In accordance with another aspect of the invention,

a nonlinear circuit is provided for use in a feedback circuit forcontrol of the roll motor of an aircraft which includes first and secondtransistors having like electrodes connected. A bias voltage is appliedacrossv the device, with circuitry provided to supply a varying signalinput to the like electrodes of the transistors. Each of the transistorsis operable to become conductive in response to a signal input of adifferent polarity. Output terminals are provided across the transistorwhereby a nonlinear output signal is produced in dependence upon therelative magnitudes of the voltage bias and the signal input.

In accordance with a more specific aspect of the invention, a nonlinearcircuit is provided including first and second transistors of oppositeconductivity type having the emitters thereof commonly connected in acomplementary configuration. Structure is provided to supply apreselected bias voltage to the bases of the transistors. Structure isprovided to supply an input signal to the commonly connected emitters ofthe transistors. Output terminals are connected to the collectors of thetransistors to receive nonlinear output signals.

DESCRIPTION OF THE DRAWINGS For a more complete understanding of thepresent invention and for further objects and advantages thereof,reference is now made to the following description taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a diagrammatic illustration of the approach and intercept ofan aircraft according to the present invention;

FIG. 2 is a combined schematic and block diagram of the basic lateralguidance system of the invention;

FIG. 3 is a schematic diagram of a portion of the system shown in FIG.2; and

FIG. 4 is a schematic diagram of the remainder of the system shown inFIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, atransmitter 10 transmits a directional radio signal identified by thedotted lines 12ab. The center line of the directional radio beam isidentified by the line 14. The transmitter 10 may comprise eithera'conventional omni or localizer transmitting station which operates inthe well-known manner.

It is the object of the invention to guide the aircraft identifiedgenerally by the numeral 16 to a preselected intercept with the centerline 14, and then to perform selected automatic operations on theguidance of the aircraft as the aircraft approaches the transmitterstation 10. In the operation of the system, the aircraft 16 travels thepath 18 which is initially about 45 to the center line 14. Thisintercept angle is gradually reduced to about 22 just before interceptis made with the center line 14 at point A. The aircraft is thendirected along the line 14 toward the transmitter 10.

At the intercept at point A, cross wind correction is applied to theguidance of the aircraft in order to compensate for cross winds. Afterintercept, the aircraft continues along the center line 14 toward thetransmitter 10 until point B, which is reached after a preselected firsttime interval after intercept. At point B, which generally occurs afterfrom 10-20 seconds after intercept, the gain of the guidance signalapplied to the aircraft 16 is reduced in half. This is done to softenthe effect of the guidance control of the aircraft to provide a morecomfortable ride after the aircraft is on course. When the aircraftreaches point C, which occurs at a second preselected time intervalafter intercept, the permissible bank angle of the aircraft is limited.In the preferred embodiment, ninety seconds after intercept,

the bank limits of the aircraft are reduced from approximately toapproximately 7, in order to eliminate wild banking excursions of theaircraft when the aircraft flies over the transmitter 10. It will beunderstood that the time intervals and control functions described maybe varied to accommodate various operating characteristics of differentaircraft.

FIG. 2 illustrates a combination schematic and block diagram of thepresent lateral guidance control system for an aircraft for operation inthe radio mode. Circuitry for operation in a heading mode (withoutradio) and in a reverse mode for flying the back course of a localizerradio beam) will be described in detail with respect to FIGS. 3 and 4.In operation in the radio mode, course information is fed through anormally closed switch arm 20 and through a" resistor 22 to a summingpoint 24. The course signal may be derived from a conventional omnicourse pickup and is representative of craft displacement from aselected ground track. A high pass filter comprising a resistor 26 and aparallel connected capacitor 28 is connected across the switch 20 forinsertion into the course input when the switch 20 is opened. A radiosignal representative of the deviation of the aircraft from the selectedradio beam is fed via a resistor 30 and via a series connected capacitor32 and resistor 34 to the summing point 24. The combined course andradio signals are fed to an operational amplifier 36, the output ofwhich is fed to an inverter circuit 38. A resistor 40 is normallyconnected across the operational amplifier 36. A switch 42 and aresistor 44 are also connected across the operational amplifier 36. Uponclosure of the normally open switch 42, the resistor 44 is thrown acrossthe amplifier 36 in order to reduce the gain thereof.

The output of the inverter circuit 38 is fed through a bank anglelimiter circuit 46 which is normally set to provide a preselected bankangle control to the aircraft. Normally, this permissible bank angle is20.

. Limiter 46 is also operable to further limit the bank angle to a lowervalue such as approximately 7. The output guidance signal from thelimiter 46 is fed through a roll rate circuit 48 and then to a summingcircuit 50. A bank angle signal is combined at the summing circuit 50 toprovide an output via lead 52 which controls the roll motor of theaircraft. The roll motor controls the ailerons of the aircraft in thewell-known manner in order to control the lateral guidance of theaircraft.

The radio signal is also fed to a high gain amplifier 54. When theaircraft is within range of the radio beam, the radio signal fed toamplifier 54 is high enough to saturate the amplifier. As shown in theillustrated waveform in FIG. 2, a deadzone is provided in the outputcharacteristics of the amplifier 54 to enable intercept with the radiobeam while flying closely parallel to the beam. The output from theamplifier 54 is fed via a lead 56 to a switch arm 58. Normally, switcharm 58 is connected to a terminal ofa resistor 60, the other terminal ofwhich is connected to the summing point 24. When the switch arm 58 isconnected to the output of amplifier 54, a false radio signal is appliedto the summing point 24 from amplifier 54 in order to introduce apreselected minimum intercept angle into the guidance signal for theaircraft. In the preferred embodiment, this false radio signal isrepresentative of an intercept angle of approximately 22%. Switch arm 58may be switched into contact with a terminal 62 which is connected to alead 64 in order to remove the effect of the high gain amplifier 54 fromthe circuit.

The output of amplifier 54 is also fed through an absolute value circuit66, the output of which is applied to a flip-flop circuit 68. Theflip-flop circuit 68 is operated when the amplifier 54 senses theintercept of the aircraft with the center line of the directional radiobeam. The output of flip-flop 68 is applied to a switch 70 which controlthe position .of the switch arm 58 and switch arm 20. Additionally, theoutput of the flip-flop 68 is applied to a twenty second delay circuit72 which operates a switch 74. Switch 74 controls the operation of thenormally open switch 42. The output of the flipflop 68 is furtherapplied to a ninety second delay circuit 76 which controls a switch 78.Switch 78 controls the operation of the bank angle limiter between thetwo prescribed bank limits. A reset network 80 is connected between thecourse input and the amplifier 54, and is responsive to large increasesin rate and amplitude in order to cause reseting of some of the controlfeatures of the system.

The basic operation of the invention in the radio mode will beunderstood by reference to FIGS. 1 and 2. When the aircraft l6approaches within range of the directional radio beam emitted from thetransmitter 10, the radio and course signals are summed at point 24 inorder to provide an initial guidance signal for directing the aircraft16 at an intercept angle of approximately 25. Additionally, thedetection of the radio beam by the high gain amplifier 54 causes theamplifier 54 to become saturated, therefore introducing a false radiosignal into the summing point 24 to provide an additional interceptangle of approximately 22% to the aircraft. Thus, upon initial detectionof the directional radio beam, aircraft 16 is directed at an approximate45 intercept angle with the center line 14 of the radio beam. As theaircraft l6 approaches the center line 14 of the radio beam, the radioerror signal is reduced, thereby reducing the intercept angle of theaircraft. Just before the aircraft reaches the center line of the radiobeam, the aircraft bank intercept angle will have been reduced toapproximately the 22% provided by the high gain amplifier 54.

When the aircraft reaches close proximity with the radio beam orintercepts center line 14 of the radio beam, the high gain amplifier S4senses the intercept and will, after a deadzone, generate a saturatedoutput signal of opposite polarity. This change in polarity is sensed bythe absolute value circuit 66 which causes the flip-flop 68 to changestate. Transition of the flipflop 68 actuates the switch 70 which thenswitches the switch arm 58 into contact with the terminal 62. Switch 70also opens the switch arm 20 at this time. Thus, the high gain amplifier54 is essentially removed from the circuit to thereby remove the falseradio indication which provided the artificial 22% intercept angle tothe aircraft. The opening of the switch arm 20 introduces the high passfilter comprising the resistor 26 and the capacitor 28 into the coursesignal, thereby providing a small steady state heading signal tocompensate for cross wind deviation of the aircraft.

The output from the flip-flop 68 is provided with a twenty second delayby the circuit 72, after which the switch 74 is operated to close theswitch arm 42. Closing of the switch arm 42 introduces the resistor 44across the amplifier 36, thereby reducing the gain of the amplifier 36by one-half. This reduction in gain of limit to approximately a 7 bankangle limit. This limitation in bank angle is provided to prevent wildexcursions of the aircraft as the aircraft flies over the transmitter10.

The high gain for the system provided when the switch arm 42 is in itsnormal position may be'obtained after intercept by resetting thecircuit. This may be done by changing from radio to heading mode andthen back to radio mode. Manually changing the course also resets theswitch 74 in order to open switch arm 42.

Referring to FIGS. 3 and 4, the circuitry is shown in schematic detailand includes circuitry for operation in heading, radio or reverse modes.For operation in the heading mode, heading signals are fed via aresistor 100 and 102 through a field effect transistor 104. A capacitor106 is connected in parallel with a diode 108 across flop.

the transistor 104 and a resistor 110. The heading signals are fed tothe input of an amplifier 112 whose output is fed via a resistor 114 tothe input of a unity gain amplifier 116. Amplifiers 112 and 116 maycomprise any suitable integrated circuit amplifier, such as the circuitsmanufactured and sold by Motorola Inc. The ,output from amplifier 116 isfed via a resistor 117 to act as a roll command signal for portions ofthe circuitry shown in FIG. 4. A relay arm 120 is operable between twopositions by a'solenoid coil 121, to selectively provide an inverted ornoninverted output for the signals fed into the amplifier 116. A reversesignal may be applied to coil 121 via lead 119.

A resistor 122 is connected in parallel with a capacitor 124 across theamplifier 112. A resistor 126 is con nected in series with a fieldeffect transistor 128 also across the amplifier l 12. Transistor 128acts as a switch to selectively control the gain of amplifier 112 byselective insertion of resistor 126 in parallel with the amplifier 112.v

For operation of the system in the radio mode, a left/- right radiosignal representative of the deviation of the aircraft from the selecteddirectional radio beam is fed via a resistor 130 and capacitor 131through resistors 132 and 134 to a terminal of a field effect transistorswitch 136. The radio signals may be fed through transistor 136 to aninput of amplifier 112. The radio signals are also fed to a summingpoint 138 for combination with course signals. The guidance signalamplified by amplifier 112 is fed to the unity gain amplifier 116 forproduction of a roll command signal. Capacitors 140 and 142 areconnected between the resistors 132 and 134 to ground.

The radio signal is also fed via a resistor 144 to a field effecttransistor 146. The radio signal is also fed to the input of anoperational amplifier 148. The output of the amplifier 148 is fedthrough a resistor 149 to a field effect transistor 150, one terminal ofwhich is connected to the summing point 138 to receive a course signalfed via resistors 152 and 154 through a switch arm 156. a high passnetwork 157 is connected across switch arm 157. The output of theamplifier 148 is also fed through a resistor 158 to the base of atransistor 162 and from thence to a transistor 164. The output fromthetransis- The gate of the field effect transistor 146 is connected viaa lead 168 through a diode 170 and a resistor 171 to the base of atransistor 172. A collector of the transistor 172 controls theenergization of a solenoid coil 174. Energization of the solenoid coil174 controls the operation of the switch arm 156.

The collector of the transistor 162 is also fed via a diode and aresistor 182 to the base of a transistor 184. A capacitor 181 isconnected between the base and collector of transistor 184. A resistor183 is connected to the collector of transistor 184. A resistor 185 isconnected across diode 180 and resistor 182. The collector of thetransistor 162 is further connected via resistors 186 and 188 to atransistor 190. The collector of transistor 190 is connected through adiode 191 to the gate of transistor 128. The base of transistor 190 isconnected via a resistor 192 to one terminal of the solenoid coil 174for control thereof. A heading mode signal is fed via resistor 194 tothe base of a transistor 196. The collector of the transistor 196 is fedto a terminal of the field effect transistor 104. The heading modesignal is also fed through a diode 198 to a terminal of the field effecttransistor 136 for control thereof. The

heading mode signal is further fed through resistors 200 and 202 to thetransmitter 190. A capacitor 203 is tied to the cathode of diode 191 andto a terminal of transistor switch 128.

The collector of the transistor 162 is connected through a Zener diode206 and resistor 207 to the base of a transistor 208. The collector oftransistor 208 is connected through a resistor 210 and a lead 212 toreceive a heading mode signal through a resistor 214. The collector ofthe transistor 208 is also fed through a resistor 216 to the base of atransistor 218. The base of transistor 218 is connected to resistor 219.The output from transistor 218 is applied through a resistor 220 to alead 222 to the right bank switching terminal. The base of transistor208 is coupled through a resistor 223 to the base of a transistor 224,the collector of which is connected through a resistor 226 and via alead 228 to the left bank switching terminal. Positive voltage biassupply is fed to the circuit via the lead 230 from a suitable source.

The course signal applied to the circuit is also fed through a resistor240 and through back-to-back capacitors 242 and 244 to the input of anoperational amplifier 246. The heading signal is also applied via aresistor 248 and through back-to-back Zener diodes 250 and 252 to theinput of the amplifier 246. The output from the amplifier 246 is appliedthrough a resistor 254 to the base of a transistor 256 and through aresistor 258 to the base of a transistor 260. The collector oftransistor 256 is connected through a resistor 257 to resistor 165. Theemitters of the transistors "256 and 260 are connected via a lead 262 tothe emitter of the heading mode transistor 196.

Approach mode command signals are fed via a resistor 264 to the base ofa transistor 266, the output of which is applied through a diode 268 toa terminal of a field effect transistor 270. The radio signal is fed viacapacitors 265 and resistor 267 to the transistor 270.

The course signal is fed to a terminal of the field effect transistor270 via lead 272. The collector of transistor 266 is also appliedthrough a resistor 272 through two parallel diodes 274 and 276 to aterminal of another field effect transistor 278 connected in series withthe transistor 270. A resistor 273 connects the anode of diode 276 tothe collector of transistor 266. A localizer switch signal is applied toa lead 280 connecting diodes 274 and 276 to the transistor 278.

Referring to FIG. 4, an amplifier 300 receives signals and feeds anoutput via resistor 302 which is applied to the bases of complementarytransistors 304 and 306. The emitters of transistors 306 and 304 areconnected to the bases of a second pair of complementary transistors 308and 310. The emitters of transistors 308 and 310 are tied via resistors312 to the input of the amplifier 300. The collector of transistor 304is applied via lead 314 to the collector of the transistor 316.

Transistor 316 is connected through a resistor 318 to a complementarytransistor 320. The emitters of transistors 316 and 320 are respectivelycoupled to the bases of complementary transistors 322 and 324. Theinverting input of amplifier 300 is applied through resistor 330 toground, and the inverting input of an operational amplifier 334 is alsoapplied to ground through a resistor 335. The output of amplifier 334 isapplied through a resistor 336 to a common connection with the bases oftransistors 316 and 320. The emitters of transistors 322 and 324 aretied via a lead 338 to a common connection with emitters ofcomplementary transistors 340 and 342. The bases of transistors 340 and342 are commonly connected, with a resistor 344 tied between theemitters and the bases of the transistors. A variable bias is applied tothe bases of the transistors via a resistor 343.

Transistors 340 and 342 and their associated circuitry constitute anovel nonlinear circuit for use with the present invention in a mannerto be subsequently described. Diodes 348 and 350 are connected in seriesacross the collectors of the transistors 340 and 342. The output fromthe nonlinear network is fed via the resistors 352 and 354 to thenoninverting input of the amplifier 334. Resistors 356 and 358 may beselectively connected into the output of the nonlinear circuit byoperation of a switch arm 360. Resistor 352 is coupled to ground bycapacitor 359. The output of the amplifier 324 is fed via the resistor336, and the resulting guidance signal to the roll motor is applied fromthe emitters of transistors 322 and 324 via a lead 364.

A left bank switch signal lead 366 is connected to the base of atransistor 368. The collector of transistor 368 is connected to thecollector of a transistor 370, the base of which is connected to lead372 on which appears the left bank switch signal. A right bank limitsignal is applied via lead 374 through a resistor 376 to the base oftransistor 368. A left bank limit signal is applied through lead 378 andthrougha resistor 380 to the base of transistor 370. Transistors 368 and370 make up the bank limiter circuit of the invention.

A roll command signal is fed via lead 382 to a roll rate circuitcomprising a transistor 384 having its collector connected in serieswith a diode 386, and a transistor 388 having its collector tied inseries to a diode 390. A resistor 392 is connected in series with acapacitor 394 and a diode 396 across the circuit. The cathode of thediode 396 is tied across the base and the emitter of transistor 384.Similarly, a diode 398 is connected in series with a capacitor 400 and aresistor 402. The diode 398 is tied across the base and the emitter ofthe transistor 388.

A 5H2 signal is fed via lead 408 to a diode bridge 410 which comprisesfour semiconductor diodes connected in a bridge configuration. A 5H2reference signal is also fed to the bridge 410. The output of the bridgeis fed via a resistor 412 to the base of the transistor 414. A

roll signal is fed via lead 416 through a capacitor 418 and a resistor420 connected to the emitter of the transistor 414. The emitter of thetransistor 414 is also connected through a resistance 422 and 424 to theinput of an amplifier 426. A roll trim signal is fed through resistor427 to amplifier 426. The output of the amplifier 426 is fed via a lead428 to a point 430 tied to three parallel resistors 432, 434 and 436.The output of amplifier 426 is connected to a resistor 429 alsoconnected to the amplifier input. Capacitors 433 are connected in serieswith resistor 432. The output of the resistor 436 is tied via lead 438to an input of the amplifier 300. The outputs of the resistors 432 and434 are fed via a lead 440 to the input of the amplifier 334. Theoutputs of the resistors 432-436 are connected through resistors 442 and444 through a lead 446 to the roll command signal lead 382.

HEADING MODE OPERATION The operation of the present invention will firstbe described when the system is set in the Heading Mode. In this mode,no radio signals are utilized, but only a heading signal which issupplied from a conventional heading bug system. This heading signal isfed through resistors and 102 through the transistor 104. The fieldeffect transistor switch 104 is operated by the transistor 196 which isenergized by the Heading Mode signal fed via the resistor 194. In theHeading Mode, the transistor acts as a closed switch and allows headingsignals to be fed to the input of the amplifier 112. The sensitivity ofthe heading signal is set by resistor 102. Resistor 100 and capacitor106 comprise a decoupling circuit that works to suppress noise spikes.

The amplified signal from the amplifier 112 is fed into the amplifier116 which is a unit gain amplifier. Relay switch arm 120 is controlledby the relay coil 121 in order to switch the signal into either theinverting or noninverting input of the amplifier. In the Heading Mode,the switch arm 120 is opened in order to feed the signal into thenoninverting input of the amplifier through resistor 114. The outputvoltage provided by the amplifier 116 is of the same amplitude and samepolarity of the input signal. The output of the amplifier 1 16 is fedthrough a resistor 1 17 which acts as a sag element for the rolldelimiter shown in FIG. 4.

The roll command signal is fed from the resistor 117 to the lead 382(FIG. 4). The signal is fed via resistor 376 to the bank limitingcircuit comprising transistors 368 and 370. These two transistors arenormally biased off, with the biases adjustable from potentiometers, notshown, so that the maximum bank capability of the aircraft may becontrolled. This circuit provides a nominal adjustment of about 20 ofbank, and may be adjustable from l5 to 25. The transistor 368 clamps thevoltage level from the signal amplifiers to a point where the right bankis limited. Transistor 370 is operable to limit the left bank. A reversebias is placed upon the bases of the transistors, with the roll commandsignals fed through the emitters thereof. When the roll command signalexceeds the bias, the particular transistor is turned on and the signalvoltage is limited at that point. From the bank limiting network, thelimited signal is fed into a roll rate network made up of two parallelintegrators comprising transistors 384 and 388 with capacity feedback.Diodes 386 and 390, in combination with the emitter base turn onpotential of the transistors 384 and 388, provide an area of slightlyless than one volt around a null where there is no delay in the inputsignals applied. Thus, fast control action is provided for a small banksignal. If the bank command signal is off null and greater than slightlyless than one volt, one of transistors 384 or 388 will conduct dependingupon the polarity of the signal. The conduction of one of these Itransistors will allow the signal to increase at a much slower rate thannormal, thereby keeping the aircraft from going into a bankuncomfortably fast if the aircraft happens to be a fast respondingairframe. It should be noted that although the voltage is allowed torise very slowly in this circuit, the voltage may go back to zero veryfast, so that the aircraft is allowed to roll out of the bank for goodcontrol action.

An attitude signal is fed from an attitude gyro, not shown, and is fedvia lead 416 to the synchronous chopper detector circuit comprisingtransistor 414 and diode bridge circuit 410. The H2 signals applied tothe bridge at 410 control the operation of the synchronous chopperdetector. The chopped signal is amplified by the amplifier 426, the gainof the amplifier being set by resistors 427 and429. The amplified signalfrom the amplifier 426 is fed through a resistor 434 to a resistor 442,wherein the attitude signal is mixed with the autopilot signal fed vialead 446. The attitude signal fed to the resistor 442 is proportional tothe rate of change through resistor 432 and capacitors 433.

After the heading signal and the attitude signal have been mixed, theyare fed to the input of amplifier 334 which serves as the preamplifierfor the servo amplifier. This amplifier is operated at a very high openloop gain and drives the servo amplifier comprising complementary pairtransistors 316, 320, 322 and 324. The output from these transistors isfed to drive the roll motor of the aircraft.

An important aspect of the invention is the nonlinear circuit comprisingdiodes 348 and 350 and transistors 340 and 342. If the output of theservo amplifier increases very slowly to the starting voltage of theroll 'motor, the roll motor moves the control cables which moves theailerons for control of the airplane. The preamplifier 334 is operatedat a very high gain so that a small error signal will eventually beamplified to the point where it will cause the roll motor to run.However, if a larger error signal occurs, the nonlinear network causesthe motor not to run immediately at full speed. Thus, as soon as theroll motor starts, an output is provided from the nonlinear network andis provided to the input of the preamplifier 334 in order to reduce thegain of the amplifier. 1

Thus, the output from the servo amplifier is fed via lead 338 to theemitters of the transistors 340 and 342. The conduction point of thetransistors 322 and 324 may be adjusted to the starting voltage of anyspecific roll motor by the variance of the roll threshold signal appliedvia resistor 343. This variance of the bias signal is accomplished withthe use of a potentiometer, not shown. As the starting potential ofservo motors vary slightly from aircraft to aircraft, the presentinvention thus enables very accurate nonlinear control of the rollmotors which has not heretofore been available.

The diodes 348 and 350 act as isolation circuits to keep the desiredvoltages from being fed to the collectors of the transistors and causingleakage through the transistors. The output of the nonlinear circuit isfed through resistor 352 to the input of the preamplifier 334. Ifdesired, the switch 360 may be utilized to switch resistors 356 or 358into the output of the nonlinear circuit. The resistors are connectedthrough capacitors 359 to ground in order to cause a delay in thefeedback so'that a small error signal will cause the roll motor to runfull speed until the aircraft has assumed its proper attitude. Then thecapacitors 359 will charge to reduce the speed of the roll motor.

MODE OPERATION When it is desired to operate the present circuit in theRadio Mode, the heading mode signal is eliminated and the field effecttransistor switch 104 is thus opened. The signal from the heading bug isthen not allowed to flow into the amplifier 112. The field effect switch136 is closed in the Radio Mode, thereby allowing radio course and ratesignals to be fed into the input of the amplifier 112 via resistors 132and 134. Resistor and capacitor 131 comprise a noise decoupling networkfor the radio signals. Resistors 132 and 134 and capacitors and 142comprise a RC delay network which causes a small amount of delay in theleft/right radio signal. This delay network also assists in removingnoise from a noisy radio signal.

The course signal is fed from an omni radio course pickup, not shown,and is fed through resistors 152 and capacitor 153 which comprises anoise decoupling network.'Resistor 154 sets the gain for the coursesignal. The relay arm 156 is controlled by the energization of thesolenoid coil 174 and is closed during intercept operation of theaircraft. When the relay arm 156 is closed, a steady state course signalwill be fed through to mix with the left/right radio signal at themixing point 138.

Also during intercept, the left/right radio signal is fed to thenoninverting input of amplifier 148 which is operated with an open loopgain. Just a few millivolts of offcenter radio signals fed into theinput of the amplifier 148 will cause this amplifier to completelysaturate.

Amplifier 148 thus serves as the high gain amplifier 54 disclosedin FIG.2 which provides the false radio signal during intercept of theaircraft. The output of the am plifier 148 is the same polarity of theradio signal error, however, the output of the amplifier 148 is a fulll2 volt signal instead of the few millivolt input signal. The output ofthe amplifier 148 will remain at a full l2 volts as long as there is anerror input.

Normally, the aircraft begins intercept with a full scale radiodeflection error which would be many times the voltage required to causesaturation of the amplifier 148. The output of this amplifier 148 is fedthrough resistor 149 and through the transistor which acts as a closedswitch at all times during intercept. The current fed from amplifier 148through resistor 149 is sufficient to cause approximately 225 headingvariation which is applied through the field effect transistor 150 tothe mixing point 138. The current through resistors 132 and 134 at theinitiation of intercept provide an additional 25 of heading deviation.The combination of signals from resistors 132 and .134 and resistor 149is thus sufficient to cause an initial total heading deviation ofapproximately 45.

Upon initiation of intercept, in the manner shown in FIG. 1, theaircraft l6 begins its intercept at an intercept angle of 45. As theradio becomes off full scale peg, or as the radio signal error decreasesas the aircraft approaches the radio course, the voltage fed to resistor132 and 134 decreases proportional to the movement of the aircrafttoward the radio source Thus, the heading deviation of the aircraft fedto the amplifier 112 will begin decreasing proportionally down to 22%plus the radio heading provided by the amplifier 148.

As the aircraft crosses the center of the radio course, the output ofthe amplifier 148 will come quickly off saturation, go through zero andsaturate in the opposite direction. This output of the amplifier 148 isfed through a resistor 158 to an absolute value detector made up oftransistor 160 and its associated circuitry. When the amplifier 148 issaturated, the voltage on the collector of the transistor 160 will bezero or slightly negative. However, during the transition when theoutput of the amplifier 148 goes from one polarity to another duringintercept with the radio course center, a positive voltage appears onthe collector of the transistor 160.

This positive voltage is coupled to the base of one side of a flip-flopcircuit made up of transistors 162 and 164. Transistor 162 is normallyoff during intercept of the aircraft. When the collector of thetransistor 160 goes positive, transistor 162 turns on and due to theregenerative feedback, the transistor 164 turns off. After transistor162 turns on, the collector of the transistor 164 goes to a highpositive voltage and this voltage is fed to the gate of the field switch150 to thereby close the transistor switch. This turning off of thetransistor 150 removes the output from the amplifier 148 from the inputof the amplifier 112. Thus, the false radio minimum intercept signal 22r is removed.

At the same time that transistor 150 is biaeed off, the

voltage on the collector of transistor 162 has been maintaining fieldeffect transistor 146 in an off condition. However, at intercept of thecenter of the radio beam, the collector of the transistor 162 goes toapproximately zero volt and thus transistor 146 is turned on. The inputto transistor 146 is a high resistance 144 which is connected directlyto the left/right radio signal. Thus, after the removal of the 22%intercept signal, an equivalent signal is fed to the summing point fromthe left/right radio signal through the transistor 146. While a delayhas heretofore been provided to the radio signal due to resistors 132and 134 and capacitors 140 and 142, the network comprising resistor 144and transistor 146 is now connected in parallel to provide an undelayedsignal. Thus, an instantaneous effect is provided by the signal fedthrough resistor 144 and transistor 146, while a slightly delayed signalis fed through the network comprising resistors 132 and 134 andcapacitors 140 and 142.

As previously noted, just prior to intercept with the center of theradio beam, transistor 162 was biased off and the collector voltagethereof was a relatively high positive voltage. This-positive voltagewas being felt through a resistor 171 to the base of the transistor 172.Transistor 172 was biased on to thereby energize the solenoid coil 174.Energization of the coil 174 maintained the solenoid switch arm 156 inthe illustrated position to provide the steady state course signal formixing with the radio signal. At intercept, the transistor I62 collectordrops to zero to to thereby turn the transistor 172 off. Solenoid coil174 is thus de-energized and the switch arm 156 is opened. This throwsthe high pass network 157 into the course signal input to provide a verysmall amount of steady state information to the circuit. Thus, at thistime the aircraft may assume a crab angle necessary to fly in a crosswind if such is present during intercept.

As the aircraft approaches the center of the radio beam duringintercept, the left/right radio signal decreases in amplitude toindicate that the aircraft is coming on course. This rate of change inthe voltage is coupled through capacitor 265 and resistor 267. This rateof change causes the transistor 266 to be turned on which in turn biasesthe field effect transistor 270 on. The rate of change information isthen coupled into the mixing point 138 through the transistor 270. It ismixed with the steady state radio and course signals.

When the aircraft is placed in an omni mode, the 10- calizer switch line280 will be provided with a high positive voltage. This high positivevoltage is coupled through diodes 2 74 and 276 to the gate of the fieldeffect transistor switch 278, opening the transistor gate 278. In thelocalizer mode, the voltage lead 280 will be zero and transistor 278will be biased on and additional rate information will be coupledthrough transistor 265 and resistor 267. Thus, twice the gain of thenormal rate of change on the left/right radio indication will beprovided. Basically, transistor 270 acts as a closed switch in theapproach mode. In the nave mode, transistor 278 acts as a closed switchduring intercept and for ninety seconds after intercept to enable theaircraft to get on the radio course and stabilized in the nave mode.Then the transistor 270 will act as an open switch and take all the rateinformation out as the aircraft is in an omni nave mode. However, if theaircraft at that time is in a localizer nave mode, the aircraft willstill be provided with half the normal rate of change coupled throughthe transistor 278.

As the aircraft intercepts with the center of the radio beam, theflip-flop circuit comprised of transistors 162 and 164 transitions,thereby causing the transistor 172 to turn off. The collector oftransistor 172 goes positive and the positive voltage is fed throughresistor 192 to the base of the transistor 190. Transistor is thusturned on. Prior to the biasing on of the transistor 190, the collectorof the transistor having had a high positive voltage. This high positivevoltage was coupled through the diode 191 resistor 202 and capacitor 203and to the gate of the field effect transistor switch 128. As thetransistor 190 is biased on, and as collector goes to approximately zerovoltage, the capacitor 203 is charged to the high positive voltage.Capacitor 203 then begins the discharge through the resistor 202.

As capacitor 203 discharges from the high positive voltage to the firingvoltage of the transistor 128, the transistor 128 turns on. When thetransistor 128 turns on, an additional resistor 126 is thrown across theamplifier 112 to thereby cut the gain of the amplifier 112 in half. Thisreduction of the gain of amplifier 112 is done to soften the effect ofthe control of any error signals on the aircraft. Tight control isrequired for the aircraft during intercept, but it is desirable tosoften this control by reducing the gain of the amplifier 112 once theaircraft is on course in order to make the aircraft ride morecomfortable.

Additionally, at the point of intercept with the radio beam center, thetransition of the flip-flop comprising the transistors 162 and 164initiated a ninety second timer comprised of diode 180, capacitor 181,resistor 183 and resistor 185. When the flip-flop transition isinitiated, the voltage on the collector of transistor 184 began at zeroand increased very slowly toward a high positive voltage. The diode 206is approximately a 6 volt Zener diode, so that when the voltage on thecollector of the transistor 184 gets to approximately 6 volts, anyvoltage above 6 volts will be coupled through the diode 206.Approximately 90 seconds isrequired for the voltage on the collector ofthe transistor 184 to reach approximately 6 volts. After this 90seconds, the output is fed through resistor 207 to the base of thetransistor 208. Transistor 208 will be turned on and its collector willgo to approximately zero voltage. When transistor 208 was turned off,the collector was in a high positive voltage which had been fed back tothe' to the negative voltage supply. Transistor 218 is thus turned on.The output from the 90 second delay timer circuit is fed to resistor 207and is also fed to'resistor 223 to cause transistor 224 to be turned on.The collectors of transistors 218 and 224 are connected through leads222 and 228 to the leads 374 and 378 on FIG. 4, in order to limit thebank angle of the aircraft. This bank limiting is caused by reducing thevoltage on the bases of transistors 368 and 370 in FIG. 4 to limit thetransistors in a lower level. The maximum signal felt on the emitters ofthe transistors 368 and 370 will allow only approximately a 7 bank, ascompared to the previous bank allowed.

The remainder of the operation of the circuitry in the radio modeapproximates the operation of the circuitry while in the Heading Modefor control of the aircraft.

REVERSE MODE OPERATIQN The operation of the aircraft when in a reversemode operation is basically identical to the approach mode up throughthe output of the amplifier 112 in FIG. 3. In the reverse mode, a highpositive voltage is fed via lead 119 to the solenoid coil 121 forenergization thereof. The relay switch arm 120 will then switch theoutput of the amplifier ll2'to the inverting input of the amplifier 116.If the aircraft is under a localizer radio beam, and the aircraft isflying on the back course thereof, the radio signals are reversed and inorder to normally fly the aircraft, the output of the amplifier 112 mustbe fed through the inverting input of the amplifier 116. Thus, only thepolarity of the guidance signals fed through the resistor 117 arechanged.

In the omni tracking mode, after the aircraft has gone through the radiointercept, the flip-flop transistors 162 and 164 have transitioned, andthe solenoid 174 has been opened to take'the steady state radio coursesignal out of the circuit, it may be desired to change the radial of theomni which is being flown. If a large change is made, it is necessary toreset the circuit back into the intercept configuration in order to getthe steady state course information and also to obtain the desirabledynamics for intercepting a new radial. As you turn the omni bearingselector knob of the aircraft, the rate of change and the voltage of thecourse pickoff is coupled through resistors 240 and capacitors 242 and244. If this rate of change is approximately 9 per second or greater,the signal is coupled into amplifier 246 and the output from thisamplifier is sufficient to cause an output from the absolute valuedetector transistor 260 and its associated circuitry. The output fromthis detector will be coupled into transistor 256 to turn transistor 256off. The collector of transistor 256 will then become positive and thispositive voltage will be coupled through resistor 257 to the base oftransistor 164. Thus, the flip-flop circuits 162 and 164 are reset backto the original intercept configuration. The timing sequence previouslydescribed will then begin all over when the aircraft intercepts the newomni radial which has been selected. 7

Additionally, if for some reason the aircraft should be disposed inas'much as a 45 heading deviation from the omni radio which has beenselected, and the aircraft is in a very slow rate of change less than 90per second, the rate circuit comprising resistor 240, capacitor 242 andthe associated circuitry does not cause sufficient output from theamplifier 246 to reset the circuit intercept. Thus, when the aircraft isin a 45 slow change situation, the steady state voltage from the coursepickoff and the aircraft will be coupled through resistor 248 and Zenerdiodes 250 and 252 to the input of the amplifier 246. The steady statesignal will then cause an output from transistors 260 and 256 in orderto reset the circuit.

Whereas the present invention has been described with respect tospecific embodiments thereof, it will be understood that various changesand modifications will be suggested by one skilled in the art, and it isintended to encompass those changes and modifications as fall within thescope of the appended claims.

I claim:

l. A lateral guidance system for an aircraft comprising:

a. amplifying means for amplifying a combined directional radio andcourse signal,

b. means operable for directing the aircraft toward a directional radiobeam at a selected intercept angle,

0. means for introducing cross wind correction to the aircraft inresponse to intercept with said radio beam,

d. means for reducing the gain of said amplifying means after a firstpreselected time interval from the intercept with said radio beam, and

e. means for limiting the permissible bank angle of the aircraft after asecond preselected time interval from the intercept with said radiobeam.

2. The guidance system of claim I and further comprising:

means for proportionally reducing said selected intercept angle to aresidual level in response to approach of the aircraft toward said radiobeam.

3. The guidance system of claim 1 wherein said means for introducingcross wind correction comprises:

a high pass heading network.

4. The guidance system of claim 1 wherein said selected intercept angleis approximately 45.

5. The guidance system of claim 4 wherein said selected intercept isreduced to approximately 22 as the aircraft approaches said radio beam.

6. The guidance system of claim 1 wherein said first time interval isapproximately seconds.

7. The guidance system of claim 1 wherein said second time interval isapproximately 90 seconds.

8. An aircraft lateral guidance system comprising:

a. summing means for summing a first signal representative of thedetection of a directional radio beam with a second signal containingcourse information,

b. amplifier means for amplifying the output of said summing means,

c. means responsive to the output of said amplifier means forcontrolling the guidance of the aircraft toward an intercept with saidradio beam,

d. means responsive to said first signal for decreasing the angle ofintercept down to a preset minimum intercept angle as the aircraftapproaches said radio beam, and

e. means responsive to intercept with said radio beam for reducing saidminimum intercept angle and for directing the aircraft along said radiobeam.

9. The system of claim 8 wherein said preset minimum intercept angle isdetermined by a high gain saturable amplifier.

10. The system of claim 9 wherein said means responsive to interceptcomprises:

an absolute value network connected to the output of said high gainamplifier, and

switch means connected to said network for disconnecting said high gainamplifier from said system.

11. The system of claim 8 and further comprising:

means for introducing high pass filtering into said second signal inresponse to intercept of the aircraft with the radio beam.

12. The system of claim 8 and further comprising:

means for reducing the gain of said amplifier means after apredetermined time interval from the intercept with the radio beam.

13. The system of claim 8 and further comprising:

means for limiting the permissible bank angle of the aircraft after apreselected time interval from the intercept with the radio beam.

14. The method of lateral guidance for an aircraft with respect to adirectional radio beam comprising:

a. combining directional radio and course signals into a lateralguidance control signal,

b. introducing an intercept angle signal into said guidance controlsignal to maintain at least a selected minimum intercept angle of theaircraft during approach to the radio beam,

c. reducing the angle of intercept of the aircraft down to said selectedminimum intercept angle as the air craft approaches the radio beam, and

d. removing said intercept angle signal upon intercept with the radiobeam.

15. The method of lateral guidance in claim 14 and further comprising:

introducing cross wind correction to the aircraft in response tointercept with the radio beam.

16. The method of claim 14 and further comprising:

reducing the amplitude of said guidance control signal after apredetermined time interval from intercept with the radio beam.

17. The method of claim 14 and further comprising: limiting-thepermissible bank angle of the aircraft after a predetermined timeinterval from intercept with the radio beam.

18. A method of lateral guidance for an aircraft comprising:

a. amplifying a combined directional and course signal,

b. directing the aircraft toward a directional radio beam at a selectedintercept angle,

c. introducing cross wind correction to the aircraft in response tointercept with said radio beam,

d. reducing the gain of said amplifying means after a first preselectedtime interval from the intercept with said radio beam, and

e. limiting the permissible bank angle of the aircraft after a secondpreselected time interval from the intercept with said radio beam.

19. The guidance system of claim 2 and further comprising:

switching means for abruptly removing said residual level when theaircraft reaches the proximity of the course center line.

1. A lateral guidance system for an aircraft comprising: a. amplifyingmeans for amplifying a combined directional radio and course signal, b.means operable for directing the aircraft toward a directional radiobeam at a selected intercept angle, c. means for introducing cross windcorrection to the aircraft in response to intercept with said radiobeam, d. means for reducing the gain of said amplifying means after afirst preselected time interval from the intercept with said radio beam,and e. means for limiting the permissible bank angle of the aircraftafter a second preselected time interval from the intercept with saidradio beam.
 2. The guidance system of claim 1 and further comprising:means for proportionally reducing said selected intercept angle to aresidual level in response to approach of the aircraft toward said radiobeam.
 3. The guidance system of claim 1 wherein said means forintroducing cross wind correction comprises: a high pass headingnetwork.
 4. The guidance system of claim 1 wherein said selectedintercept angle is approximately 45*.
 5. The guidance system of claim 4wherein said selected intercept is reduced to approximately 22* as theaircraft approaches said radio beam.
 6. The guidance system of claim 1wherein said first time interval is approximately 20 seconds.
 7. Theguidance system of claim 1 wherein said second time interval isapproximately 90 seconds.
 8. An aircraft lateral guidance systemcomprising: a. summing means for summing a first signal representativeof the detection of a directional radio beam with a second signalcontaining course information, b. amplifier means for amplifying theoutput of said summing means, c. means responsive to the output of saidamplifier means for controlling the guidance of the aircraft toward anintercept witH said radio beam, d. means responsive to said first signalfor decreasing the angle of intercept down to a preset minimum interceptangle as the aircraft approaches said radio beam, and e. meansresponsive to intercept with said radio beam for reducing said minimumintercept angle and for directing the aircraft along said radio beam. 9.The system of claim 8 wherein said preset minimum intercept angle isdetermined by a high gain saturable amplifier.
 10. The system of claim 9wherein said means responsive to intercept comprises: an absolute valuenetwork connected to the output of said high gain amplifier, and switchmeans connected to said network for disconnecting said high gainamplifier from said system.
 11. The system of claim 8 and furthercomprising: means for introducing high pass filtering into said secondsignal in response to intercept of the aircraft with the radio beam. 12.The system of claim 8 and further comprising: means for reducing thegain of said amplifier means after a predetermined time interval fromthe intercept with the radio beam.
 13. The system of claim 8 and furthercomprising: means for limiting the permissible bank angle of theaircraft after a preselected time interval from the intercept with theradio beam.
 14. The method of lateral guidance for an aircraft withrespect to a directional radio beam comprising: a. combining directionalradio and course signals into a lateral guidance control signal, b.introducing an intercept angle signal into said guidance control signalto maintain at least a selected minimum intercept angle of the aircraftduring approach to the radio beam, c. reducing the angle of intercept ofthe aircraft down to said selected minimum intercept angle as theaircraft approaches the radio beam, and d. removing said intercept anglesignal upon intercept with the radio beam.
 15. The method of lateralguidance in claim 14 and further comprising: introducing cross windcorrection to the aircraft in response to intercept with the radio beam.16. The method of claim 14 and further comprising: reducing theamplitude of said guidance control signal after a predetermined timeinterval from intercept with the radio beam.
 17. The method of claim 14and further comprising: limiting the permissible bank angle of theaircraft after a predetermined time interval from intercept with theradio beam.
 18. A method of lateral guidance for an aircraft comprising:a. amplifying a combined directional and course signal, b. directing theaircraft toward a directional radio beam at a selected intercept angle,c. introducing cross wind correction to the aircraft in response tointercept with said radio beam, d. reducing the gain of said amplifyingmeans after a first preselected time interval from the intercept withsaid radio beam, and e. limiting the permissible bank angle of theaircraft after a second preselected time interval from the interceptwith said radio beam.
 19. The guidance system of claim 2 and furthercomprising: switching means for abruptly removing said residual levelwhen the aircraft reaches the proximity of the course center line.